Electrolytic production of alkali metals



Aug. 24 1-926.

O P.E.HAYNES ELECTROLYTIC PRODUCTION OF ALKALI METALS Filed March 25}1922 I especially a Patented Aug. 24, 1926.

UNITED STATES Y 1,591,231 PATENT OFFICE.

PIERRE E. HAYNES, OF BUFFALO, NEW YORK.

ELECTROLYTIC PRODUCTION OF ALKALI IETALB.

Application filed Iarch 23, 1922. Serial Io. 545,918.

The chief object of this invention is to provide a process for themanufacture of alkali metals, particularly sodium, potassium andmagnesium, whereby such metals may be produced in greater purity and'ata higher eiiiciency than by present methods.

The alkali metals are now commonly made by the electrolysis of molten orfused solutions of their compounds. The chief difliculty of the presentprocesses is the protection of the metal from atmospheric oxygen andnitrogen as well as from some of the byproducts of the electrolytlcdecomposition itself.

My invention in its preferred form consists in electrolyzing moltencompounds containing the desired metal, removing some or all of theproducts including the metal as vapors and afterwards condensing themetal se arately.

aking magnesium as a specific exam le, fused carnallite or any suitablecompoun of magnesium is melted and electrolyzed at a suitabletemperature, preferably above 650 degrees centigrade, in an air-tightvessel capable of withstanding an external pressure of, say, oneatmosphere or more. The

nmgnesium will evaporate if the internal pressure is reduced to lessthanone inch of mercury, and the evaporation is at a sufli cie'nt rateto remove it from the solution rapidly. It will of course evaporate at alesser rate if the pressure in the cell is great- At the lower pressure,however, the reaction between magnesium and various gases is greatlyreduced in intensity due to the greater attenuation of the gasesandmagnesium vapor. The result is a larger yield of metal and theocclusion of less of these gases in the metal produced.

Sod1um, ota ssium, and magnesium are dhpted to treatment by this processon account of their low melting and boiling points. The generallyaccepted melting and boiling points of these materials are as follows:

Each of these metals is easily va orized at several hundred degreesbelow its oiling point if the pressure 1s sufliciently reduced.

Apparatus convenient and suitable for practicing the inventionin thepreferred manner "is illustrated diagrammatically in the accompanyingdrawing, in which the a paratus is shown partly in section.

Referring to the drawin ,1 is a closed electrolytic cell partially filed with a molten electrolyte 2 containing one or more compounds of themetal desired. The electroyte is separated into two ortions near thesurface by a porcelain or ot er suitable hood or partition 3. Uponsubjection of the mass to a direct or continuous current between cathode4 and anode 5, preferably composed of iron and carbon, respectively, themetal is produced around the cathode and certain gaseous by-products aregenerated around the anode. The gaseous portions of the anodic productsare withdrawn through valved pipe 6 by vacuum pump 7. Due to the lowspecific gravity of the metallic prodnot it rises to the surface of themolten liquid around cathode 4 and there vaporizes. The vapors arewithdrawn through valved pipe 8 to condenser 9 which is exposed to thecoolin effect of the atmosphere or any other heat a sorbing medium. Thevapor of the metal withdrawn into condenser 9 by the vacuum pump 7acting through pipe 10 is liquefied and falls into receptacle 11 whichis removably attached to condenser 9. The liquefied metal product isretained in receptacle ll until'the end of the run and is then recoveredby detaching receptacle 11 at thepoint 12 and withdrawingthe roduct ineither the liquid or solid con ition.

Where an extremely low pressure is attainable or where an extremely puremetal is not desired, the hood 3 may be dispensed with and all of theproducts of the electrolysis drawn through pipe 8 and condenser 9 wherethe metal will be deposited by condensation and the uncondensed vaporswithdrawn through pipe 10 by vacuum pump 7.

Some additional heat may be required for the evaporation of the metalproduct and it is therefore desirable in some cases to utilize'more orless of the heat of condensation to maintain or aid in maintaining thetemperature of cell 1, or to su ply this extra heat by the use of suitale auxiliary means. As indicative of the latter method a gas burner isshown at 13.

The use of a vacuum electrolytic cell not only excludes air but aspreviously stated diminishes the occlusion of the gases by the metal andthe recombination of the gases .and metal. Both these results arebelieved chlorid from sea water or terrestrial brines,

sponding potassium compounds are also usacommonly known as bittern.These residues nearly always contain all the alkali metals. For themanufacture of sodium it is also ssible to use sodium hydroxid, sodiumcarnate or sodium nitrate, and the correbio for makin that metal, but atpresent their cost is in gpneral prohibitive. In some cases, especia ywhen using naturally occurring mixtures containing the salt or salts, itis desirable to add one or more substances to obtain a suitable oradvantageous melting point or prevent side react-ions. Among thesubstances suitable for such purl pose may be mentioned sodium chlorid,so-

ium sulfid, ammonium chlorid, and calciumfluorid. It is generallydesirable to operate at a rather higher temperature than has commonlybeen emplo ed heretofore, in order to get the increase vapor tensionwhich is'an advantage in the present process but which in the past hasbeen a source of loss and'annoyance.

The voltage-and current employed may i varyconsiderably', depending uponthe usual factors, such as the resistance of the bath; the size of thecell and the effectiveness of the heat-insulation. used with it, if any;the amount, of heat supplied from. an external source, if any; etc.Hence no general rule A asto voltage and current can be given. It

maybe stated, however, that formaking magnesium fromcarnalhte withextraneous .heat, a voltage of 501- 6 volts is sutficient, l with acurrent densityof from 10 to 15 amtraneous heat it is generallydesirable to operate with 8 to 10 volts or higher and 40- or moreamperes persquare decimeter.

. atmospheric.

a temperature above the melting point of the metal, and withdrawing theanodic and cathodic products in vapor or gaseous form at less thanatmospheric pressure.

3. A process for the production of metals, comprising electrolyzing amolten bath containing a compound of the metal desired, at a temperatureabove that of the melting point of the metal, and withdrawing the anodicand cathodic products in vapor or gaseous form separately at a pressureless than atmospheric.

41. A process for the production of metals, comprising electrol zingamoltenbath con taining a-compoun of the metal desired, at a temperatureat which the metal has an appreciable vapor tension, and withdraw ingthe anodic and cathodic products in vapor or gaseous form, at a pressurebelow 5. A process for the production of metals,

comprising electrolyzing a molten bath containinga compound 0 the metaldesired,

at a temperature at which the metal has an appreciable vapor tension andwithdrawing the .anodicand cathodic products sepa- I rately in vapor orgaseous form at a pressure below atmospheric.

6. A process for making magnesium, com-- prising electrolyzing a fusedsalt of magnesium at a temperature sufiicient to vaporize themagnesiumproduced, withdrawing the anodic and cathodic products separately invapor or gaseous form, and condensing the magnesium vapor so withdrawn.

In testimony whereof I hereto afiix my signature.

PIERRE E. HAYNES.

